Unilaterally mat, sealable, uv-stabilized, flame resistant, co-extruded, biaxially oriented polyester film, method for the production and the use thereof

ABSTRACT

The invention concerns a unilaterally mat, sealable, UV-stabilized and flame-resistant, sealable, co-extruded, biaxially oriented polyester film comprising at least one base layer (B) and a sealable top coating (A) applied to both sides of said base layer, in addition to a mat covering (C). The film also contains at least one UV stabilizer as a light stabilizer. The invention further concerns a method for the production of said film and the use thereof.

[0001] The invention relates to a sealable, UV-resistant, coextruded,biaxially oriented polyester film which has one matt side and iscomposed of at least one base layer B and of, applied to the two sidesof this base layer, a sealable outer layer A and a matt outer layer C.The film also comprises at least one UV stabilizer as light stabilizer.The invention also includes the use of the film and a process for itsproduction.

[0002] GB-A 1 465 973 describes a coextruded polyester film having twolayers, one layer of which consists of copolyesters containingisophthalic acid and terephthalic acid, and the other layer of whichconsists of polyethylene terephthalate. The patent gives no usefulindication of the sealing performance of the film. The lack ofpigmentation means that the film cannot be produced by a reliableprocess (cannot be wound up) and that the possibilities for furtherprocessing of the film are limited.

[0003] EP-A 0 035 835 describes a coextruded, sealable polyester filmwhere, in the sealable layer, particles whose average size exceeds thesealable layer thickness are present in order to improve winding andprocessing performance. The particulate additives form surfaceprotrusions which prevent undesired blocking and sticking of the film torolls or guides. No further details are given concerning theincorporation of antiblocking agents in relation to the other,nonsealable layer of the film. It is uncertain whether this layercomprises antiblocking agents. The choice of particles having diametersgreater than that of the sealable layer, at the concentrations given inthe examples, impairs the sealing performance of the film. The patentdoes not give any indication of the sealing temperature range of thefilm. The seal seam strength is measured at 140° C. and is in the rangefrom 63 to 120 N/m (from 0.97 N/15 mm to 1.8 N/15 mm of film width).

[0004] EP-A 0 432 886 describes a coextruded multilayer polyester filmwhich has a surface on which has been arranged a sealable layer, and hasa second surface on which has been arranged an acrylate layer. Thesealable outer layer here may also be composed ofisophthalic-acid-containing and terephthalic-acid-containingcopolyesters. The coating on the reverse side gives the film improvedprocessing performance. The patent gives no indication of the sealingtemperature range of the film. The seal seam strength is measured at140° C. For a sealable layer thickness of 11 μm the seal seam strengthgiven is 761.5 N/m (11.4 N/15 mm). A disadvantage of the reverse-sideacrylate coating is that this side is now not sealable with respect tothe sealable outer layer, and the film therefore has only veryrestricted use.

[0005] EP-A 0 515 096 describes a coextruded, multilayer, sealablepolyester film which comprises a further additive in the sealable layer.The additive may comprise inorganic particles, for example, and ispreferably distributed in an aqueous layer onto the film during itsproduction. Using this method, the film is claimed to retain its goodsealing properties and to be easy to process. The reverse side comprisesonly very few particles, most of which pass into this layer via therecycled material. This patent again gives no indication of the sealingtemperature range of the film. The seal seam strength is measured at140° C. and is above 200 N/m (3 N/15 mm). For a sealable layer of 3 μmthickness the seal seam strength given is 275 N/m (4.125 N/15 mm).

[0006] WO 98/06575 describes a coextruded, multilayer polyester filmwhich comprises a sealable outer layer and a nonsealable base layer. Thebase layer here may have been built up from one or more layers, and theinner layer of these layers is in contact with the sealable layer. Theother (outward-facing) layer then forms the second nonsealable outerlayer. Here, too, the sealable outer layer may be composed ofisophthalic-acid-containing and terephthalic-acid-containingcopolyesters, but these comprise no antiblocking particles. The filmalso comprises at least one UV absorber, which is added to the baselayer in a ratio of from 0.1 to 10% by weight. The base layer hasconventional antiblocking agents. The film has good sealability, butdoes not have the desired processing performance and also hasshortcomings in optical properties. The film may also have a mattsurface, but then has high haze, which is undesirable.

[0007] Films in which no UV-absorbing materials are present exhibityellowing and impairment of mechanical properties after even a shortperiod in outdoor applications, due to photooxidative degradation bysunlight.

[0008] Good mechanical properties include a high modulus of elasticity(E_(MD)>3200 N/mm²; E_(TD)>3500 N/mm²) and good values for tensilestress at break (in MD>100 N/mm²; in TD>130 N/mm²).

[0009] It was an object of the present invention to eliminate thedisadvantages of the prior art.

[0010] The invention provides a UV-resistant, sealable, coextruded,biaxially oriented polyester film with one matt side and with at leastone base layer B, and with a sealable outer layer A, and with another,matt, outer layer C, where at least one layer comprises a UV absorberand where the sealable outer layer A has a minimum sealing temperatureof 110° C. and a seal seam strength of at least 1.3 N/15 mm, and thetopographies of the two outer layers A and C are characterized by thefollowing features: sealable outer layer A:

[0011] R_(a) value <30 nm

[0012] value measured for gas flow 500-4000 s nonsealable, matt outerlayer C:

[0013] 200 nm<R_(a)<1000 nm

[0014] value measured for gas flow <50 s.

[0015] The invention further relates to the use of the film and to aprocess for its production.

[0016] A transparent, UV-resistant, sealable, and biaxially orientedpolyester film with one matt side is therefore provided and inparticular has very good sealability, is cost-effective to produce, hasimproved processability, and has improved optical properties.

[0017] The invention permits the sealing range of the film to beextended to low temperatures, the seal seam strength of the film to beincreased, and at the same time better handling of the film to beprovided than in the prior art. It has also been ensured that the filmis capable of processing even on high-speed machinery. Regrind arisingdirectly during production of the film can be reintroduced to theextrusion process at a concentration of up to 60% by weight, based onthe total weight of the film, without any significant resultant adverseeffect on the physical properties of the film.

[0018] Since the film of the invention is particularly intended foroutdoor applications and/or critical indoor applications, it is to havehigh UV resistance. High UV resistance means that sunlight or other UVradiation causes no, or only extremely little, damage to the films. Inparticular, when used outdoors for a number of years films should showno yellowing, embrittlement, or surface-cracking, and should haveunimpaired mechanical properties. High UV resistance means that the filmabsorbs UV light and does not begin to transmit light until the visibleregion has been reached.

[0019] The UV stabilizer(s) is/are advantageously fed directly in theform of masterbatch(es) during film production, the concentration of theUV stabilizer(s) preferably being in the range from 0.01 to 5.0% byweight, with preference from 0.1 to 3.0% by weight, based on the weightof the respective layer of the polyester used.

[0020] The film of the invention generally has at least three layers,the layers encompassed then being the base layer B, the sealable outerlayer A, and the matt outer layer C.

[0021] At least 90% by weight of the base layer B of the film isgenerally composed of a thermoplastic polyester. Polyesters suitable forthis purpose are those made from ethylene glycol and terephthalic acid(polyethylene terephthalate, PET), from ethylene glycol andnaphthalene-2,6-dicarboxylic acid (polyethylene 2,6-naphthalate, PEN),from 1,4-bishydroxymethylcyclohexane and terephthalic acid(poly-1,4-cyclohexanedimethylene terephthalate, PCDT), or else made fromethylene glycol, naphthalene-2,6-dicarboxylic acid andbiphenyl-4,4′-dicarboxylic acid (polyethylene 2,6-naphthalatebibenzoate, PENBB). Preference is given to polyesters of which at least90 mol %, preferably at least 95 mol %, is composed of ethylene glycolunits and terephthalic acid units, or of ethylene glycol units andnaphthalene-2,6-dicarboxylic acid units. The remaining monomer unitsderive from other aliphatic, cycloaliphatic or aromatic diols and,respectively, dicarboxylic acids, as may also occur in the layer A (orthe layer C).

[0022] Other examples of suitable aliphatic diols are diethylene glycol,triethylene glycol, aliphatic glycols of the formula HO—(CH₂)_(n)—OH,where n is an integer from 3 to 6 (in particular 1,3-propanediol,1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) and branchedaliphatic glycols having up to 6 carbon atoms. Among the cycloaliphaticdiols, mention should be made of cyclohexanediols (in particular1,4-cyclohexanediol). Examples of other suitable aromatic diols have theformula HO—C₆H₄—X—C₆H₄—OH, where X is —CH₂—, —C(CH₃)₂—, —C (CF₃)₂—, —O—,—S— or —SO₂—. Bisphenols of the formula HO—C₆H₄—C₆H₄—OH are also verysuitable.

[0023] Other aromatic dicarboxylic acids are preferablybenzenedicarboxylic acids, naphthalene dicarboxylic acids (such asnaphthalene-1,4- or -1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylicacids (in particular biphenyl-4,4′-dicarboxylic acid),diphenylacetylene-x,x′-dicarboxylic acids (in particulardiphenylacetylene-4,4′-dicarboxylic acid) or stilbene-x,x′-dicarboxylicacids. Among the cycloaliphatic dicarboxylic acids mention should bemade of cyclohexanedicarboxylic acids (in particularcyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylicacids, the C₃-C₁₉ alkanediacids are particularly suitable, and thealkane moiety here may be straight-chain or branched.

[0024] One way of preparing the polyesters is the transesterificationprocess. Here, the starting materials are dicarboxylic esters and diols,which are reacted using the customary transesterification catalysts,such as the salts of zinc, of calcium, of lithium, of magnesium or ofmanganese. The intermediates are then polycondensed in the presence ofwell known polycondensation catalysts, such as antimony trioxide ortitanium salts. Another equally good preparation method is the directesterification process in the presence of polycondensation catalysts.This starts directly from the dicarboxylic acids and the diols.

[0025] The sealable outer layer A applied by coextrusion to the baselayer B has been built up on the basis of polyester copolymers andessentially consists of amorphous copolyesters composed predominantly ofisophthalic acid units and of terephthalic acid units, and of ethyleneglycol units. The remaining monomer units derive from other aliphatic,cycloaliphatic or aromatic diols and, respectively, dicarboxylic acids,as may also occur in the base layer. Preferred copolyesters whichprovide the desired sealing properties are those which have been builtup from ethylene terephthalate units and from ethylene isophthalateunits and from ethylene glycol units. The proportion of ethyleneterephthalate is from 40 to 95 mol %, and the corresponding proportionof ethylene isophthalate is from 60 to 5 mol %. Preference is given tocopolyesters in which the proportion of ethylene terephthalate is from50 to 90 mol % and the corresponding proportion of ethylene isophthalateis from 50 to 10 mol %, and particular preference is given tocopolyesters in which the proportion of ethylene terephthalate is from60 to 85 mol % and the corresponding proportion of ethylene isophthalateis from 40 to 15 mol %.

[0026] The preferred embodiment of the matt outer layer C comprises ablend or a mixture made from two components I and II, and, if desired,comprises additives in the form of inert inorganic antiblocking agents.

[0027] Component I of the mixture or of the blend is a polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer or amixture made from polyethylene terephthalate homo- or copolymers.

[0028] Component II of the copolymer or of the mixture or of the blendis a polyethylene terephthalate copolymer which is composed of thecondensation product of the following monomers or of their derivativescapable of forming polyesters:

[0029] A) from 65 to 95 mol % of isophthalic acid;

[0030] B) from 0 to 30 mol % of at least one aliphatic dicarboxylic acidhaving the formula HOOC (CH₂)_(n)COOH, where n is from 1 to 11;

[0031] C) from 5 to 15 mol % of at least one sulfomonomer containing analkali metal sulfonate group on the aromatic moiety of a dicarboxylicacid;

[0032] D) the stoichiometric amount of a copolymerizable aliphatic orcycloaliphatic glycol having from 2 to 11 carbon atoms needed to form100 mol % of condensate;

[0033] each of the percentages given being based on the total amount ofthe monomers forming component II. For a detailed description ofcomponent II see also EP-A-0 144 878, which is expressly incorporatedherein by way of reference.

[0034] For the purposes of the present invention, mixtures aremechanical mixtures which are prepared from the separate components. Forthis, the separate constituents are generally combined in the form ofsmall-dimensioned compressed moldings, e.g. lenticular or bead-shapedpellets, and mixed with one another mechanically, using a suitableagitator. Another way of producing the mixture is to feed components Iand II in pellet form separately to the extruder for the outer layer ofthe invention, and to carry out mixing in the extruder and/or in thedownstream systems for melt transportation.

[0035] For the purposes of the present invention, a blend is analloy-like composite of the separate components I and II which can nolonger be separated into the initial constituents. A blend hasproperties like those of a homogeneous material and can therefore becharacterized by appropriate parameters.

[0036] The ratio (ratio by weight) of the two components I and II of theouter layer mixture or of the blend can be varied within wide limits anddepends on the intended use of the multilayer film. The ratio ofcomponents I and II is preferably in the range from I:II=10:90 toI:II=95:5, preferably from I:II=20:80 to I:II=95:5, and in particularfrom I:II=30:70 to I:II=95:5.

[0037] The desired sealing properties, the desired degree of mattness,and the desired processing properties of the film of the invention areobtained by combining the properties of the copolyester used for thesealable outer layer with the topographies of the sealable outer layer Aand of the nonsealable, matt outer layer C.

[0038] The minimum sealing temperature of 110° C. and the seal seamstrength of at least 1.3 N/15 mm are achieved when the copolymersdescribed in more detail above are used for the sealable outer layer A.The films have their best sealing properties when no other additives, inparticular no inorganic or organic fillers, are added to the copolymer.In this case, with the copolyester given above, the lowest minimumsealing temperature and the highest seal seam strengths are obtained.However, the handling of the film is poor in this case, since thesurface of the sealable outer layer A has a marked tendency to block.The film can hardly be wound and has little suitability for furtherprocessing on high-speed packaging machinery. To improve handling of thefilm, and processability, it is necessary to modify the sealable outerlayer A. This is best done with the aid of suitable antiblocking agentsof a selected size, which are added to the sealable layer at aparticular concentration, and specifically in such a way as to firstlyminimize blocking and secondly give only insignificant impairment ofsealing properties. This desired combination of properties can beachieved when the topography of the sealable outer layer A ischaracterized by the following set of parameters:

[0039] The roughness of the sealable outer layer, characterized by theR_(a) value, is generally less than 30 nm, preferably less than 25 nm,otherwise the sealing properties are adversely affected for the purposesof the present invention.

[0040] The value measured for gas flow should be from 500 to 4000 s,preferably from 600 to 3500 s. At values below 500 s the sealingproperties are adversely affected for the purposes of the presentinvention, and at values above 4000 s the handling of the film becomespoor.

[0041] The nonsealable, matt outer layer C is characterized by thefollowing set of parameters:

[0042] The roughness of the matt outer layer, characterized by the R_(a)value, is in the range from 200 to 1000 nm, preferably from 220 to 900nm. Values below 200 nm have an adverse effect on the winding andprocessing performance of the film, and on the degree of mattness of thesurface. Values above 1000 nm impair the optical properties (haze) ofthe film.

[0043] The value measured for gas flow should be ≦50 s, preferably ≦45s. At values above 50 the degree of mattness of the film is adverselyaffected.

[0044] The UV stabilizers selected for rendering the film of theinvention UV-resistant may in principle be any organic or inorganic UVstabilizers suitable for incorporation within polyesters. Suitable UVstabilizers of this type are known from the prior art and are describedin more detail in WO 98/06575, in EP-A-0 144 878, in EP-A-0 031 202,EP-A-0 031 203 or in EP-A-0 076 582, for example.

[0045] UV stabilizers, i.e. light stabilizers which are UV absorbers,are generally chemical compounds which can intervene in the physical andchemical processes of light-induced degradation. Carbon black and otherpigments can give some protection from light. However, these substancesare unsuitable for transparent films, since they cause discoloration orcolor change. The only compounds suitable for transparent films arethose organic or organometallic compounds which produce no, or onlyextremely slight, color or color change in the thermoplastic to bestabilized.

[0046] Suitable UV stabilizers are those which absorb at least 70%,preferably 80%, particularly preferably 90%, of the UV light in thewavelength region from 180 to 380 nm, preferably from 280 to 360 nm.These are particularly suitable if they are thermally stable in thetemperature range from 260 to 300° C., i.e. do not decompose and do notcause evolution of gas. Examples of suitable UV stabilizers are2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickel compounds,salicylic esters, cinnamic ester derivatives, resorcinol monobenzoates,oxanilides, hydroxybenzoates, sterically hindered amines and/ortriazines, preferably the 2-hydroxybenzotriazoles and the triazines.

[0047] In one preferred embodiment, the film of the invention comprises,as UV-absorbing substance, from 0.01 to 5.0% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or from 0.01 to5.0% by weight of2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol).It is also possible to use a mixture of these two UV stabilizers or amixture of at least one of these two UV stabilizers with other UVstabilizers, and here the total concentration of light stabilizer ispreferably from 0.01 to 5.0% by weight, based on the weight of thethermoplastic polyester.

[0048] In the three-layer embodiment, the UV stabilizer is preferablypresent in the nonsealable outer layer C. However, if required, the baselayer B or the sealable outer layer A may also have UV stabilizers. Theconcentration of the stabilizer(s) here is based on the weight of thethermoplastics in the layer which has UV stabilizer(s).

[0049] Surprisingly, weathering tests to the test specification ISO 4892using the Atlas CI65 Weather-Ometer have shown that, to improve UVresistance, in the case of the abovementioned three-layer film it isfully sufficient for the outer layers of thickness from 0.3 to 2.5 μm tohave UV stabilizers.

[0050] Weathering tests have shown that when films have been renderedUV-resistant according to the invention they generally show noyellowing, no embrittlement, no loss of surface gloss, no surfacecracking and no impairment of mechanical properties even after anextrapolated 5 to 7 years of outdoor application in weathering tests.

[0051] The light stabilizer may be fed straightaway when thethermoplastic is prepared, or it may be fed into the extruder duringfilm production.

[0052] It is preferable for the light stabilizer to be added by way ofmasterbatch technology. The additive is first fully dispersed in acarrier material. Carrier materials which may be used are the actualthermoplastic used, e.g. polyethylene terephthalate, or else otherpolymers sufficiently compatible therewith. After feeding into thethermoplastic for film production, the constituents of the masterbatchmelt during the extrusion process and thus become dissolved in thethermoplastic.

[0053] The concentration of the UV absorber alongside the thermoplasticin the masterbatch is from 2.0 to 50.0% by weight, preferably from 5.0to 30.0% by weight, the constituents always giving 100% by weight intotal.

[0054] An important factor in masterbatch technology is that theparticle size and the bulk density of the masterbatch are similar to theparticle size and bulk density of the thermoplastic, enablinghomogeneous dispersion and thus homogeneous UV resistance.

[0055] A film of this type is therefore also cost-effective.

[0056] It is moreover very surprising that regrind produced from thefilms or from the moldings is reusable without any adverse effect on theYellowness Index of the film.

[0057] The base layer B may also comprise customary additives, such asstabilizers and/or antiblocking agents. The two other layers A and C mayalso comprise these additives. It is appropriate for these to be addedto the polymer or, respectively, polymer mixture straight away prior tomelting. Examples of stabilizers used are phosphorus compounds, such asphosphoric acid or phosphoric esters.

[0058] Suitable antiblocking agents (in this context also termedpigments) are inorganic and/or organic particles, such as calciumcarbonate, amorphous silica, talc, magnesium carbonate, bariumcarbonate, calcium sulfate, barium sulfate, lithium phosphate, calciumphosphate, magnesium phosphate, aluminum oxide, LiF, the calcium,barium, zinc or manganese salts of the dicarboxylic acids used, carbonblack, titanium dioxide, kaolin or crosslinked polystyrene particles orcrosslinked acrylate particles.

[0059] The antiblocking agents selected may also be mixtures of two ormore different antiblocking agents or mixtures of antiblocking agents ofthe same composition but different particle size. The particles may beadded to the individual layers at the respective advantageousconcentrations, e.g. as a glycolic dispersion during thepolycondensation or by way of masterbatches during extrusion.

[0060] Preferred particles are SiO₂ in colloidal or in chain form. Theseparticles become very well bound into the polymer matrix and create onlyvery few vacuoles. Vacuoles generally cause haze and it is thereforeappropriate to avoid these. There is no restriction in principle on thediameters of the particles used. However, it has proven appropriate forachieving the object to use particles with an average primary particlediameter below 100 nm, preferably below 60 nm and particularlypreferably below 50 nm, and/or particles with an average primaryparticle diameter above 1 μm, preferably above 1.5 μm and particularlypreferably above 2 μm. However, the average particle diameter of theseparticles described last should not be above 5 μm.

[0061] To achieve the abovementioned properties of the sealable film, ithas also proven to be appropriate to select the particle concentrationin the base layer B to be lower than in the two outer layers A and C. Ina three-layer film of the type mentioned the particle concentration inthe base layer B will be from 0 to 0.15% by weight, preferably from0.001 to 0.12% by weight and in particular from 0.002 to 0.10% byweight. There is no restriction in principle on the diameter of theparticles used, but particular preference is given to particles with anaverage diameter above 1 mm.

[0062] In its advantageous usage form, the film of the invention iscomposed of three layers: the base layer B and, applied on both sides ofthis base layer, outer layers A and C, and outer layer A is sealablewith respect to itself and with respect to outer layer C.

[0063] To achieve the property profile mentioned for the film, the outerlayer C has more pigment (i.e. higher pigment concentration) than theouter layer A. The pigment concentration in this second, matt outerlayer C is from 1.0 to 10.0%, advantageously from 1.5 to 10% and inparticular from 2.0 to 10%. In contrast, the other outer layer A, whichis sealable and positioned opposite to the outer layer C, has a lowerdegree of filling with inert pigments. The concentration of the inertparticles in layer A is from 0.01 to 0.2% by weight, preferably from0.015 to 0.15% by weight and in particular from 0.02 to 0.1% by weight.

[0064] Between the base layer and the outer layers there may, ifdesired, also be an intermediate layer. This may again be composed ofthe polymers described for the base layers. In one particularlypreferred embodiment, it is composed of the polyester used for the baselayer. It may also comprise the customary additives described. Thethickness of the intermediate layer is generally above 0.3 μm,preferably in the range from 0.5 to 15 μm, in particular in the rangefrom 1.0 to 10 μm and very particularly preferably in the range from 1.0to 5 μm.

[0065] In the particularly advantageous three-layer embodiment of thefilm of the invention, the thickness of the outer layers A and C isgenerally above 0.1 μm, and is generally in the range from 0.2 to 4.0μm, advantageously in the range from 0.2 to 3.5 μm, in particular in therange from 0.3 to 3 μm and very particularly preferably in the rangefrom 0.3 to 2.5 μm, and the thicknesses of the outer layers A and C maybe identical or different.

[0066] The total thickness of the film of the invention may vary withincertain limits. It is from 3 to 100 μm, in particular from 4 to 80 μm,preferably from 5 to 70 μm, the layer B preferably making up from 5 to90% of the total thickness.

[0067] The polymers for the base layer B and the two outer layers A andC are introduced to three extruders. Any foreign bodies or contaminationpresent may be filtered out from the polymer melt prior to extrusion.The melts are then extruded through a coextrusion die to give flat meltfilms, and layered one upon the other. The multilayer film is then drawnoff and solidified with the aid of a chill roll and, if desired, otherrolls.

[0068] The film of the invention is generally produced by thecoextrusion process known per se.

[0069] The procedure for this process is that the melts corresponding tothe individual layers of the film are coextruded through a flat-filmdie, the resultant film is drawn off for solidification on one or morerolls, the film is then biaxially stretched (oriented), and thebiaxially stretched film is heat-set and, if desired, corona- orflame-treated on the surface layer intended for treatment.

[0070] The biaxial stretching (orientation) is generally carried outsequentially, and preference is given to sequential biaxial stretchingin which stretching is first longitudinal (in the machine direction) andthen transverse (perpendicular to the machine direction).

[0071] As is usual in coextrusion, the polymer or the polymer mixturefor the individual layers is first compressed and plasticized in anextruder, and any additives used may already be present in the polymeror the polymer mixture during this process. The melts are thensimultaneously extruded through a flat-film die (slot die), and theextruded multilayer film is drawn off on one or more take-off rolls,whereupon it cools and solidifies.

[0072] The biaxial orientation is generally carried out sequentially,preferably orienting first longitudinally (i.e. in the machinedirection=MD) and then transversely (i.e. perpendicularly to the machinedirection=TD). This gives orientation of the molecular chains. Thelongitudinal orientation can be carried out with the aid of two rollsrunning at different speeds corresponding to the desired stretchingratio. For the transverse orientation use is generally made of anappropriate tenter frame.

[0073] The temperature at which the orientation is carried out may varyover a relatively wide range and depends on the film properties desired.The longitudinal stretching is generally carried out at from 80 to 130°C., and the transverse stretching at from 90 to 150° C. The longitudinalstretching ratio is generally in the range from 2.5:1 to 6:1, preferablyfrom 3:1 to 5.5:1. The transverse stretching ratio is generally in therange from 3.0:1 to 5.0:1, preferably from 3.5:1 to 4.5:1. Prior to thetransverse stretching, one or both surfaces of the film may be in-linecoated by known processes. The in-line coating may serve, for example,to give improved adhesion of the metal layer or of any printing inkapplied, or else to improve antistatic performance or processingperformance.

[0074] For producing a film with very good sealing properties it hasproven advantageous for the planar orientation Δp of the film to be lessthan Δp0.165, but particularly less than Δp0.163. In this case thestrength of the film in the direction of its thickness is so great thatwhen the seal seam strength is measured it is specifically the seal seamwhich separates, and the tear does not enter the film or propagatetherein.

[0075] The significant variables affecting the planar orientation Δphave been found to be the longitudinal and transverse stretchingparameters, and also the SV value of the raw material used. The processparameters include in particular the longitudinal and transversestretching ratios (λ_(MD) and λ_(TD)), the longitudinal and transversestretching temperatures (T_(MD) and T_(TD)), the film web speed and thenature of the stretching, in particular that in the longitudinaldirection of the machine. For example, if the planar orientationobtained with a machine is Δp0.167 with the following set of parameters:λ_(MD)=4.8 and λ_(TD)=4.0, a longitudinal stretching temperature T_(MD)of from 80-118° C. and a transverse stretching temperature T_(TD) offrom 80-125° C., then increasing the longitudinal stretching temperatureT_(MD) to 80-125° C. or increasing the transverse stretching temperatureT_(TD) to 80-135° C., or lowering the longitudinal stretching ratioλ_(MD) to 4.3 or lowering the transverse stretching ratio λ_(TD) to 3.7gives a planar orientation Δp within the desired range. The film webspeed here was 340 m/min and the SV value for the material was about730. For the longitudinal stretching, the data mentioned are based onwhat is known as N-TEP stretching, composed of a low-orientationstretching step (LOE, Low Orientation Elongation) and a high-orientationstretching step (REP, Rapid Elongation Process). Other stretchingsystems in principle give the same ratios, but the numeric values foreach process parameter may be slightly different. The temperatures givenare based on the respective roll temperatures in the case of thelongitudinal stretching and on infrared-measured film temperatures inthe case of the transverse stretching.

[0076] In the heat-setting which follows, the film is held for from 0.1to 10 s at a temperature of from 150 to 250° C. The film is then woundup in a usual manner.

[0077] After the biaxial stretching it is preferable for one or bothsurfaces of the film to be corona- or flame-treated by one of the knownmethods. The intensity of the treatment is generally in the range above45 mN/m.

[0078] The film may also be coated in order to achieve other desiredproperties. Typical coatings are layers with adhesion-promoting,antistatic, slip-improving or release action. These additional layersmay be applied to the film by way of in-line coating, using aqueousdispersions, prior to the transverse stretching step.

[0079] The film of the invention has excellent sealability, very good UVresistance, very good handling properties and very good processingperformance. The sealable outer layer A of the film seals not only withrespect to itself (fin sealing) but also with respect to the nonsealableouter layer C (lap sealing). The minimum sealing temperature for lapsealing is only about 10 K higher, and the reduction in seal seamstrength is not more than 0.3 N/15 mm.

[0080] Compared with prior art films, mattness has also been improvedwhile at the same time reducing the haze of the film. It has beenensured that regrind can be reintroduced to the extrusion process duringfilm production at a concentration of from 20 to 60% by weight, based onthe total weight of the film, without any significant resultant adverseeffect on the physical properties of the film.

[0081] The excellent sealing properties, very good handling, and verygood processing properties of the film make it particularly suitable forprocessing on high-speed machinery.

[0082] The excellent combination of properties possessed by the films ofthe invention, furthermore, makes them, and articles produced therefrom,suitable for a wide variety of different applications, for example forinterior decoration, for constructing exhibition stands or forexhibition requisites, as displays, for placards, for protective glazingof machines or of vehicles, in the lighting sector, in the fitting outof shops or of stores, or as a promotional requisite or laminatingmedium.

[0083] Good UV resistance moreover makes the film suitable for outdoorapplications, e.g. for greenhouses, or the advertising sector, roofingsystems, exterior cladding, protective coverings for materials,including the protection of metallic surfaces, e.g. of steel sheet,construction sector applications and illuminated advertising profiles.

[0084] The outer layer C has a characteristic matt, antireflectivesurface, making it particularly attractive for the applicationsmentioned.

[0085] The table below (Table 1) gives the most important filmproperties according to the invention. TABLE 1 Range accordingParticularly to the invention Preferred preferred Unit Test method Outerlayer A Minimum sealing temperature <110 <105 <100 ° C. internal Sealseam strength    >1.3 >1.5 >1.8 N/15 mm internal Average roughness R_(a) <30 <25 <20 nm DIN 4768, cut-off 0.25 mm Range of values for gas flow500-4000  800-3500 1000-3000 sec internal measurement Gloss,20° >120 >130 >140 DIN 67 530 Outer layer C COF    <0.5 <0.45 <0.40 DIN53 375 Average roughness R_(a) 200-1000 225-900 250-800 nm DIN 4768,cut-off 0.25 mm Range of values for gas flow  <50 <45 <49 sec internalmeasurement Gloss, 60°  <60 <55 <50 DIN 67 530 Other film propertiesHaze  <40 <35 <30 % ASTM D1003-52 Planar orientation     <0.1650 <0.163<0.160 internal Weathering test, UV  <20% ISO 4892 resistance Change inproperties^(i))

[0086] Each of the properties in the examples below was measured to thefollowing standards or by the following methods.

[0087] Test Methods

[0088] SV (DCA), IV (DVE)

[0089] Standard viscosity SV (DCA) is measured in dichloroacetic acid bya method based on DIN 53726. The intrinsic viscosity (IV) is calculatedas follows from the standard viscosity

IV (DCA)=6.67·10⁻⁴ SV·(DCA)+0.118

[0090] Determination of Minimum Sealing Temperature

[0091] Hot-sealed specimens (seal seam 20 mm×100 mm) are produced with aBrugger HSG/ET sealing apparatus, by sealing the film at differenttemperatures with the aid of two heated sealing jaws at a sealingpressure of 2 bar and with a sealing time of 0.5 s. From the sealedspecimens test strips of 15 mm width were cut. The T-seal seam strengthwas measured as in the determination of seal seam strength. The minimumsealing temperature is the temperature at which a seal seam strength ofat least 0.5 N/15 mm is achieved.

[0092] Seal Seam Strength

[0093] To determine seal seam strength, two film strips of width 15 mmwere placed one on top of the other and sealed at 130° C. with a sealingtime of 0.5 s and a sealing pressure of 2 bar (apparatus: Brugger modelNDS, single-side-heated sealing jaw). The seal seam strength wasdetermined by the T-peel method.

[0094] Coefficient of Friction

[0095] Coefficient of friction was determined to DIN 53 375. Thecoefficient of sliding friction was measured 14 days after production.

[0096] Surface Tension

[0097] Surface tension was determined by what is known as the ink method(DIN 53 364).

[0098] Haze

[0099] Hölz haze was measured by a method based on ASTM-D 1003-52 but,in order to utilize the most effective measurement range, measurementswere made on four pieces of film laid one on top of the other, and a 1°slit diaphragm was used instead of a 40 pinhole.

[0100] Gloss

[0101] Gloss was determined to DIN 67 530. The reflectance was measuredas an optical value characteristic of a film surface. Based on thestandards ASTM-D 523-78 and ISO 2813, the angle of incidence was set at20°. A beam of light hits the flat test surface at the set angle ofincidence and is reflected and/or scattered thereby. A proportionalelectrical variable is displayed representing light rays hitting thephotoelectronic detector. The value measured is dimensionless and mustbe stated together with the angle of incidence.

[0102] Surface Gas Flow Time

[0103] The principle of the test method is based on the air flow betweenone side of the film and a smooth silicon wafer sheet. The air flowsfrom the surroundings into an evacuated space, and the interface betweenfilm and silicon wafer sheet acts as a flow resistance.

[0104] A round specimen of film is placed on a silicon wafer sheet inthe middle of which there is a hole providing the connection to thereceiver. The receiver is evacuated to a pressure below 0.1 mbar. Thetime in seconds taken by the air to establish a pressure rise of 56 mbarin the receiver is determined.

[0105] Test Conditions: Test area 45.1 cm² Weight applied 1276 g Airtemperature 23° C. Humidity 50% relative humidity Aggregated gas volume1.2 cm³ Pressure difference 56 mbar

[0106] Determination of Planar Orientation Δp

[0107] Planar orientation is determined by measuring the refractiveindex with an Abbe refractometer in accordance with internal operationsspecification 24.

[0108] Preparation of Specimens

[0109] Specimen size and length: from 60 to 100 mm

[0110] Specimen width: corresponds to prism width of 10 mm

[0111] To determine n_(MD) and n_(α) (=n_(z)), the specimen to be testedhas to be cut out from the film with the running edge of the specimenrunning precisely in the direction TD. To determine n_(TD) and n_(α)(=n_(z)), the specimen to be tested has to be cut out from the film withthe running edge of the specimen running precisely in the direction MD.The specimens are to be taken from the middle of the film web. Care mustbe taken that the temperature of the Abbe refractometer is 23° C. Usinga glass rod, a little diiodomethane (N=1.745) ordiiodomethane-bromonaphthalene mixture is applied to the lower prism,which has been cleaned thoroughly before the test. The refractive indexof the mixture must be greater than 1.685. The specimen cut out in thedirection TD is firstly laid on top of this, in such a way that theentire surface of the prism is covered. Using a paper wipe, the film isnow firmly pressed flat onto the prism, so that it is firmly andsmoothly positioned thereon. The excess liquid must be sucked away. Alittle of the test liquid is then dropped onto the film. The secondprism is swung down and into place and pressed firmly into contact. Theright-hand knurled screw is then used to turn the indicator scale untila transition from light to dark can be seen in the field of view in therange from 1.62 to 1.68. If the transition from light to dark is notsharp, the colors are brought together using the upper knurled screw insuch a way that only one light and one dark zone are visible. The sharptransition line is brought to the crossing point of the two diagonallines (in the eyepiece) using the lower knurled screw. The value nowindicated on the measurement scale is read off and entered into the testrecord. This is the refractive index n_(MD) in the machine direction.The scale is now turned using the lower knurled screw until the rangevisible in the eyepiece is from 1.49 to 1.50. The refractive index n_(α)or n_(z) (in the direction of the thickness of the film) is thendetermined. To improve the visibility of the transition, which is onlyweakly visible, a polarization film is placed over the eyepiece. This isturned until the transition is clearly visible. The same considerationsapply as in the determination of n_(MD). If the transition from light todark is not sharp (colored), the colors are brought together using theupper knurled screw in such a way that a sharp transition can be seen.This sharp transition line is placed on the crossing point of the twodiagonal lines using the lower knurled screw, and the value indicated onthe scale is read off and entered into the table.

[0112] The specimen is then turned, and the corresponding refractiveindices n_(MD) and n_(α) (=n_(z)) of the other side are measured andentered into an appropriate table. After determining the refractiveindices in, respectively, the direction MD and the direction of thethickness of the film, the specimen strip cut out in the direction MD isplaced in position and the refractive indices n_(TD) and n_(α) (=n_(z))are determined accordingly. The strip is turned over, and the values forthe B side are measured. The values for the A side and the B side arecombined to give average refractive indices. The orientation values arethen calculated from the refractive indices using the followingformulae:

Δn=n _(MD) −n _(TD)

Δp=(n _(MD) +n _(TD))/2−n _(z)

n _(av)=(n _(MD) +n _(TD) +n _(z))/3

[0113] Surface Defects

[0114] Surface defects are determined visually.

[0115] Mechanical Properties

[0116] Modulus of elasticity, tear strength and elongation at break aremeasured longitudinally and transversely to ISO 527-1-2.

[0117] Weathering (on Both Sides), UV Resistance

[0118] UV resistance is tested as follows to the test specification ISO4892 Test apparatus: Atlas Ci65 Weather-Ometer Test conditions: ISO4892, i.e. artificial weathering Irradiation time: 1000 hours (per side)Irradiation: 0.5 W/m², 340 nm Temperature: 63° C. Relative humidity: 50%Xenon lamp: inner and outer filter made from borosilicate Irradiationcycles: 102 minutes of UV light, then 18 minutes of UV light with waterspray on the specimens, then again 102 minutes of UV light, etc.

[0119] Color Change

[0120] The change in color of the specimens after artificial weatheringis measured using a spectrophotometer to DIN 5033.

[0121] The greater the numerical deviation from standard, the greaterthe color difference. Numerical values of 0.3 can be neglected andindicate that there is no significant color change.

[0122] Yellowness

[0123] The Yellowness Index (YI) is the deviation from the colorlesscondition in the “yellow” direction, and is measured to DIN 6167.Yellowness values (YI)<5 are not visually detectable.

EXAMPLES

[0124] In the following examples and comparative examples in each caseuse films of different thickness produced by a known extrusion process.

Example 1

[0125] Chips made from polyethylene terephthalate (prepared by thetransesterification process with Mn as transesterification catalyst, Mnconcentration: 100 ppm) were dried at 150° C. to residual moisture below100 ppm and fed to the extruder for the base layer B. Chips made frompolyethylene terephthalate and from a filler were likewise fed to theextruder for the nonsealable outer layer C.

[0126] Alongside this, chips were prepared made from a linear polyesterwhich is composed of an amorphous copolyester with 78 mol % of ethyleneterephthalate and 22 mol % of ethylene isophthalate (prepared via thetransesterification process with Mn as transesterification catalyst, Mnconcentration: 100 ppm). The copolyester was dried at a temperature of100° C. to a residual moisture below 200 ppm and fed to the extruder forthe sealable outer layer A.

[0127] The UV stabilizer2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol (®Tinuvin 1577) isfed in the form of masterbatches. The masterbatches are composed of 5%by weight of Tinuvin 1577 as active component and 95% by weight ofpolyethylene terephthalate (for outer layer C) and, respectively, 95% byweight of polyethylene isophthalate (for outer layer A). The 5% byweight strength Tinuvin 1577 is fed only to the two thick outer layers,20% by weight of the respective masterbatches, by way of masterbatchtechnology.

[0128] Coextrusion, followed by stepwise longitudinal and transverseorientation, is used to produce a transparent three-layer film with ABCstructure and with a total thickness of 12 μm. The thickness of eachouter layer can be found in Table 2. Outer layer A is a mixture madefrom:  20.0% by weight of UV masterbatch based on polyethyleneisophthalate  77.0% by weight of copolyester with an SV of 800  3.0% byweight of masterbatch made from 97.75% by weight of copolyester (SV of800) and 1.0% by weight of ® Sylobloc 44 H (synthetic SiO₂ from Grace)and 1.25% by weight of ® Aerosil TT 600 (fumed SiO₂ from Degussa) Baselayer B: 100.0% by weight of polyethylene terephthalate with an SV of800 Outer layer C is a mixture made from:  20.0% by weight of UVmasterbatch based on polyethylene terephthalate  65.0% by weight ofpolyethylene terephthalate with an SV of 800 (=component I)  15.0% byweight of component II

[0129] Component II was prepared as described in more detail in Example1 of EP-A-0 144 878.

[0130] The production conditions in the individual steps of the processwere: Extrusion: Temperatures Layer A: 270° C. Layer B: 290° C. Layer C:290° C. Die gap width: 2.5 mm Take-off roll Temperature: 30° C.Longitudinal stretching: Temperature: 80-125° C. Longitudinal stretchingratio: 4.2 Transverse stretching: Temperature: 80-135° C. Transversestretching ratio: 4.0 Heat-setting: Temperature: 230° C. Duration: 3 s

[0131] The film had the required good sealing properties and the desiredmattness, and exhibits the desired handling and the desired processingperformance. The film structure and the properties achieved in filmsprepared in this way are given in Tables 2 and 3.

[0132] The films in this example, and in all of the examples below, wereweathered on both sides, in each case for 1000 hours per side, using theAtlas Ci65 Weather-Ometer to test specification ISO 4892 and then testedfor mechanical properties, discoloration, surface defects, haze andgloss.

Example 2

[0133] In comparison with Example 1, the outer layer thickness of thesealable layer A was raised from 1.5 to 2.0 μm. This has given improvedsealing properties, and in particular the seal seam strength hasincreased markedly.

Example 3

[0134] In comparison with Example 1, the film produced now had athickness of 20 μm. The outer layer thickness for the sealable layer Awas 2.5 μm and that for the nonsealable layer C was 2.0 μm. This hasagain improved sealing properties, and in particular seal seam strengthhas increased markedly, and the handling properties of the film haveimproved slightly.

Example 4

[0135] In comparison with Example 3, the copolymer for the sealableouter layer A has been changed. Instead of the amorphous copolyesterwith 78 mol % of polyethylene terephthalate and 22 mol % of ethyleneterephthalate, use was now made of an amorphous copolyester with 70 mol% of polyethylene terephthalate and 30 mol % of ethylene terephthalate.The polymer was processed in a twin-screw vented extruder, without anyneed for predrying. The outer layer thickness for the sealable layer Awas again 2.5 μm, and that for the nonsealable layer C was 2.0 μm. Thishas given improved sealing properties, and in particular the seal seamstrength has increased markedly. To achieve good handling properties andgood processing performance from the film, the pigment concentration inthe two outer layers was raised slightly.

Comparative Example 1

[0136] In comparison with Example 1, the sealable outer layer A was nownot pigmented. Although this has given some improvement in the sealingproperties, the handling properties of the film and its processingperformance have worsened unacceptably.

Comparative Example 2

[0137] In comparison with Example 1, the level of pigmentation in thesealable outer layer A was now as high as in the nonsealable outer layerC. This measure has improved the handling properties and the processingproperties of the film, but the sealing properties have worsenedmarkedly.

Comparative Example 3

[0138] In comparison with Example 1, the nonsealable outer layer A wasnow pigmented to a markedly lower level. The handling properties of thefilm and its processing performance have worsened markedly.

Comparative Example 4

[0139] Example 1 from EP-A 0 035 835 was repeated. The sealingperformance of the film, its handling properties and its processingperformance are poorer than in the examples according to the invention.TABLE 2 Pigment Film Layer thicknesses Average pigment concentrationsthickness Film μm Pigments in layers diameter in layers μm ppm Exampleμm structure A B C A B C A B C A B C E 1 12 ABC 1.5 9 1.5 Sylobloc 44 Hnone 0 2.5 2.5 300 0 0 Aerosil TT 0.04 0.04 375 600 E 2 12 ABC 2.0 8.51.5 Sylobloc 44 H none 0 2.5 2.5 300 0 0 Aerosil TT 0.04 0.04 375 600 E3 20 ABC 2.5 15.5 2.0 Sylobloc 44 H none 0 2.5 2.5 300 0 0 Aerosil TT0.04 0.04 375 600 E 4 20 ABC 2.5 15.5 2.0 Sylobloc 44 H none 0 2.5 2.5400 0 0 Aerosil TT 0.04 0.04 500 600 CE 1 12 ABC 1.5 9 1.5 none noneSylobloc 44 H 2.5 0 1200 Aerosil TT 0.04 1500 600 CE 2 12 ABC 1.5 9 1.5Sylobloc 44 H none Sylobloc 44 H 2.5 2.5 300 0 1200 Aerosil TT AerosilTT 0.04 0.04 375 1500 600 600 CE 3 12 ABC 1.5 9 1.5 Sylobloc 44 H noneSylobloc 44 H 2.5 2.5 300 0 600 Aerosil TT Aerosil TT 0.04 0.04 375 750600 600 CE 4 15 AB 2.25 12.75 Gasil 35 none 3 2500 0 EP-A 035 835

[0140] TABLE 3 Seal Coefficient seam of friction Minimum strength COFsealing side A side C Average Values Winding temperature with withroughness measured for performance side A with respect respect R_(a) gasflow Gloss and respect to to side to side side side side side side sidehandling Processing Example side A A C A C A C Δp A C Haze propertiesperformance E 1 100 2.0 0.45 25 340 1200 20 0.165 140 50 32 ++ ++ E 2 982.7 0.45 26 340 1280 20 0.165 140 50 32 ++ ++ E 3 95 3.0 0.41 23 3401110 20 0.165 130 45 34 ++ ++ E 4 85 3.3 0.40 23 340 1300 20 0.165 13045 34 ++ ++ CE 1 98 2.1 0.45 10 65 10,000 80 0.165 160 170 1.5 − − CE 2110 1.0 0.45 65 65 80 80 0.165 130 170 2.8 − − CE 3 100 2.0 0.45 25 371200 150 0.165 160 190 1.5 − − CE 4 115 0.97 >2 70 20 50 >5000 12 − −

[0141] TABLE 4 Modulus of elasticity Tear strength Elongation at N/mm²N/mm² break % Total Gloss longi- longi- longi- discoloration Surfaceside side Example Weathering tudinal transverse tudinal transversetudinal transverse value defects A C Haze E 1 Before 4300 5800 220 280170 100 140 170 2.5 After 4100 5480 190 270 150 90 0.2 none 132 165 2.8E 2 Before 4200 5600 215 260 170 100 140 170 2.5 After 4030 5400 190 250150 90 0.25 none 138 165 2.8 E 3 Before 4500 5700 230 280 175 105 130170 3.0 After 4000 5350 196 255 150 89 0.24 none 138 155 3.7 E 4 Before4300 5800 220 275 178 111 130 170 3.0 After 3900 5360 192 248 148 920.27 none 138 165 3.5

1. A sealable, UV-resistant, coextruded, biaxially oriented polyesterfilm with one matt side and with at least one base layer B based on athermoplastic polyester, and with a sealable outer layer A, and withanother matt, outer layer C, where at least one layer comprises a UVabsorber, characterized in that the sealable outer layer A has a minimumsealing temperature of 110° C. and a seal seam strength of at least 1.3N/15 mm, and the topographies of the two outer layers A and C have thefollowing features sealable outer layer A: R_(a)<30 nm value measuredfor gas flow 500 to 4000 s nonsealable, matt outer layer C: 200nm<R_(a)<1000 nm value measured for gas flow <50 s.
 2. The film asclaimed in claim 1, characterized in that the sealable outer layer Acomprises an amorphous copolyester which has been built up from ethyleneterephthalate units and ethylene isophthalate units and from ethyleneglycol units.
 3. The film as claimed in claim 1 or 2, characterized inthat the amorphous copolyester of the sealable outer layer A containsfrom 40 to 95 mol % of ethylene terephthalate and from 60 to 5 mol % ofethylene isophthalate, preferably from 50 to 90 mol % of ethyleneterephthalate and from 50 to 10 mol % of ethylene isophthalate, and inparticular from 60 to 85 mol % of ethylene terephthalate and from 40 to15 mol % of ethylene isophthalate.
 4. The film as claimed in one or moreof claims 1 to 3, characterized in that the matt outer layer C comprisesa blend or a mixture made from two components I and II and, if desired,comprises additives in the form of inert inorganic antiblocking agents.5. The film as claimed in one or more of claims 1 to 4, characterized inthat the concentration of the UV absorber is from 0.01 to 5.0% byweight, preferably from 0.1 to 3% by weight, based on the weight of therespective layer of the polyester used.
 6. The film as claimed in one ormore of claims 1 to 5, characterized in that the UV absorbers presentare 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickelcompounds, salicylic esters, cinnamic ester derivatives, resorcinolmonobenzoates, oxanilides, hydroxybenzoates, sterically hindered aminesand/or triazines, preferably 2-hydroxybenzotriazoles and triazines andin particular 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or2,2′-methylene-bis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl,-tetramethylbutyl)phenol.
 7. The film as claimed in one or more ofclaims 1 to 6, characterized in that regrind is present at aconcentration of up to 60% by weight, based on the total weight of thefilm.
 8. A process for producing a sealable, UV-resistant, biaxiallyoriented polyester film with one matt side, and with at least onepolyester film, and with at least one base layer B based on athermoplastic polyester, and with a sealable outer layer A, and alsowith a matt outer layer C, where at least one layer comprises a UVabsorber, characterized in that the melts corresponding to theindividual layers of the film are coextruded through a flat-film die,the resultant film is drawn off for solidification on one or more rolls,the film is then biaxially stretched (oriented), and the biaxiallystretched film is heat-set.
 9. The process as claimed in claim 8,characterized in that the film is corona- or flame-treated on thesurface layer intended for treatment.
 10. The process as claimed inclaim 8 or 9, characterized in that the UV absorber is fed into theextruder when the thermoplastic polymer is prepared, or during filmproduction, and is preferably fed by way of masterbatch technology. 11.The process as claimed in claim 10, characterized in that themasterbatch comprises, besides the thermoplastic, from 2.0 to 50.0% byweight, preferably from 5.0 to 30.0% by weight, of UV absorber, theconstituents always giving 100% by weight in total.
 12. The use of thefilm as claimed in one or more of claims 1 to 7 for indoor or outdoorapplications.
 13. The use as claimed in claim 12 indoors for interiordecoration, for constructing exhibition stands or for exhibitionrequisites, as displays, for placards, for protective glazing ofmachines or of vehicles, in the lighting sector, in the fitting out ofshops or of stores, as a promotional requisite or laminating medium, oroutdoors for greenhouses, in the advertising sector, roofing systems,exterior cladding, protective coverings for materials, or constructionsector applications or illuminated advertising profiles.